Spinning process with contemporaneous stretching of synthetic fibres



June 3, 1969 D. NICITA ET AL 3,448,185

SPINNING PROCESS WlTH CQNTEMPORANEOUS STRETCHING OF SYNTHETIC FIBRES Filed April 15, 1964 United States Patent US. Cl. 264-210 9 Claims ABSTRACT OF THE DISCLOSURE Melt-spun filaments of polyamide and polyesters are extruded from the spinneret into a chamber containing steam at a temperature of from 30 to 200 C. and subjected for at least one second to treatment by steam and air, the proportion of air to steam being such that the air has a relative moisture of at least 85%, are then passed into a heated space in which every portion of the yarn remains for at least one second, then the yarn is stretched mechanically immediately after its issuance from the heated space, with a stretching ratio between 1:35 and 1:5.

It is known that polyamidic fibres are produced from molten polyamide by means of extrusion through spinnerets with small holes. It is also known that in order that the polyamidic fibres should have useful applications in the extile field, they must undergo cold-stretching so as to assume a length up to five times that preceding the stretching.

The two operations of spinning and of cold-stretching are normally carried out on two distinct machines.

With the ordinary process the polyamide produced by the spinning machine is collected on cones, bobbins and the like and is allowed to become conditioned for some hours. The conditioning is a seasoning of the thread which makes it suited for the cold-stretching. The main phenomena that take place during the conditioning are good distribution of the moisture in the interior of the thread and an increase of the specific Weight due to the greater compactness caused by the internal shrinking of the polyamide. After conditioning, the thread is stretched on the stretching machine.

Said machine consists of a device for feeding the thread at constant speed by Wheels, rolls or other contrivances, and of a device for collecting the thread having a structure analogous to the feeder but with rolls revolving at higher peripheral speed. The thread becomes elongated between the feeding device and the collecting device with a stretching ratio equal to the ratio between the periph- V eral speed of the collecting device and that of the feeding device.

To the layman the union of the spinning device and of the stretching device in one single apparatus, spinning and stretching continuously, having no particular feature but the joining of the devices, may appear obvious.

In practice instead the mere coupling of the spinning machine with the stretching machine does not provide good results since it brings about a thread having characteristics for inferior to those of thread produced by the conventional methods; in particular, as will be reported in Example 1, one gets too high a number of failures.

In the opinion of I. Sandeman and A. Keller (J. of

Polymer Science XX-I, pages 401-435 (1956)) and of Howard W. Starkweather Jr. and Robert E. Moynihan (J. of Polymer Science XXII, pages 363-368 (1956)), to a specific weight of 1.1301.l35 there corresponds a percent crystallinity of the polycapron-amide equal to 25- 29% by Weight.

In normal production when spinning is carried out by machine, the yarn is seasoned and then stretched on another machine: specific weights of nylon 6 are obtained between 1.125 and 1.135, namely the thread has a good degree of crystallinity.

Now since the minimal percent crystallinity that cangive cross-links in a polyamide is about 7%, according to Howard M. Starkweather, Jr. and George E. Moore, John E. Hansen, Thomas M. Roder and Richard E. Brooks (1. of Polymer Science XXI, pages 189-204 1956) this would appear to be the minimal crystallinity necessary for the thread to be usefully stretched on a commercial machine. This opnion seemed to be supported, not only in industrial practice but also by the results obtained by other experimenters (see French Patent 976,505; US. Patent 2,604,667; Natus D. and Sauer H., Faserf. 11nd Textiltechnik 7 (1956) 10 pages 468-76; Sauer H. Faserf, u. Textiltechnik, 7 (1956), 12 pages 561-64; Natus, D., Sauer, H., and Wonderoth, H., Faserf. u. Textiltechnik, 5 (1954), 10 pages 431-34) who carried out the stretching of threads practically in the amorphous state utilizing such expedients as plastic stretching under the spinneret at high speed and utilizing for the purposes of the stretching the friction of the thread with air or analogous expedients.

Their experiences, very instructive from the point of view of theory, led in practice to obtaining yarns having characteristics inferior to those obtained by the conventional spinning method, seasoning .and stretching of the threads at high crystallinity (specific weight 1130-1135).

Also the mere coupling of the spinning machine with the stretching machine leads to an increased number of failures as reported in Example 1.

In US. Patent 3,002,804 there is also proposed a process of continuous spinning and stretching wherewitlr the filaments are rapidly cooled down to a least 40 below melting point, then are subjected to a continuously increasing stretching tension, passing them at a very low speed through a liquid bath, the filaments being extracted in the liquid bath.

In this patent it is stated that the cooling rapidity produces amorphous fibres permitting their linear orientation prior to crystallization and offering thereby away for obtaining improved tenacities with low stretching ratios. 7

Actually while said patent does not provide any data about the spinning of nylon 6, the data given about the spinning of nylon 66 indicate a maxi mum tenacity of 4.6 gr./ den. with elongations of 36-37%, and indicate that if attempts are made to diminish the elongations sensibly, sensibly improved tenacities are not obtained, but on the contrary the tenacities tend to diminish, and a yarn of lower grade is obtained. In any case, the yarn obtained is inferior to that manufactured according to the conventional process, by which it is possible to attain tenacities much more elevated, and only in particular circumstances can it become similar to the latter in quality.

Our tests have permitted constructing the curves of increase of specific weight, which as seen above is an almost linear function of the crystallinity, in function of time and of the moisture of the thread. In this way it has been possible to ascertain that the thread attains a crystallinity equivalent to the minimal percent (7%) believed necessary in order that it be stretched, in a time 3 of at least 3 minutes and with the maximum content of water.

The time of 3 minutes necessary to attain 7% of crystallinity of the polymer spun after the extrusion, represents, therefore, the minimum time that should elapse between the extrusion and the stretching; which interval of time renders a process indiustrially non-realizable that involves the simple immediate succession of the usual spinning and of the usual stretching.

At any rate there is not known so far any process or device which permits continuous spinning and immediate stretching thereafter, with high stretching ratios and obtaining those high tenacities, and more precisely, high tenacities coupled with convenient elongations, which are requested by the textile technique.

The present invention, however, makes it possible to carry out the spinning and stretching continuously, efiecting the stretching by conventional methods and, therefore, with obtainment of stretching ratios and high tenacity with good elongations, by proceeding in the following manner.

The filaments extruded in the usual way from a spinneret are treated immediately under the spinneret with steam, saturated or not saturated, at temperatures of from to 200 C. but preferably at about 100 C., for a length of time not shorter than 1 second and preferably of from 1 to 3 seconds.

The steam can be fed either admixed with air in such proportions that the relative moisture of said moist air is not lower than 85% and preferably is 90%, or by means of a nozzle passed through by the thread having the jet of steam in the direction of the movement of the thread and also in the direction opposed to the movement of the thread.

After a zone of treatment with steam the thread passes through a space having preferably the shape of a vertical tube heated externally in such a way as to have an internal temperature of from 20 to 95 C. and preferably of from 60 to 70 C. The duration of the passage of the thread in said space may vary within rather wide limits, from a fraction of seconds to several seconds, but preferably from 1 second to 6 seconds. The thread is then subjected to stretching in one or more steps according to the textile characteristics desired.

By the process according to the present invention it is possible to stretch in general all synthetic polymers, such as polyamides and polyesters and preferably nylon 6 or nylon 66 or ethylene polyterephthalate.

It has been found for example that by the process described yarns of nylon 6 (caprolactam polymer of polycapronamide) are obtained with tenacity even of 8.5 to 9.0 gr./ den. and elevated regularity of count with a minimal number of breakages even at a very considerable collecting speed, e.g. of from 400 to 2000 m./min. The spinning speeds are preferably not lower than 200 m./ min. and even more preferably of from 250 to 500 m./min.

The results obtained by the process according to the invention cannot be explained by the knowledge acquired heretofore in conventional technique.

The applicant holds that a possible explanation to which however the applicant does not intend to be bound, may be as follows.

Contrary to what was believed heretofore, the stretchability of a filament with accompanying elevated tenacities seems to be tied up not so much to the effective crystallinity than rather to an undefined property which translates itself into a crystallinity of the filament. That is to say, thefilament, though crystalline, loses however the property of attaining the desired crystallinity in a comparatively short time when subjected to the conditions of treatment according to the invention. Obviously that explanation involves the conclusion that the stretchability is derived from another property, namely from the elevated velocity of crystallization of which the crystallinity, effective and potential, is only a symptom.

The device according to the present invention therefore comprises in combination with a usual melt-spinning device at the beginning and a device for collecting the stretched yarn at the end, means for treating the extruded yarn in the vicinity of the spinneret by saturated and nonsaturated steam, and eventually air, a space for accommodating the yarn after its having been subjected to the action of steam, means for heating externally said space and means known per se for carrying out subsequently the stretching of the yarn in one or more steps.

The means for feeding steam and eventually air and the means for heating the corresponding space, as well as the dimensions of said space, should correspond to the ranges of temperature and of duration previously specified in defining the process of the present invention.

The stretching is carried out by means known per se, that is to say by mechanical means adapted to realize a well-defined and elevated stretching ratio, as with discontinuous conventional processes.

The invention will be more fully understood from the figure, which diagrammatically illustrates apparatus operating according to the invention, and from description of the non-limiting working examples.

In the figure, 10 indicates a spinneret of a spinning head (not shown in the figure), 11 indicates a chamber in which the thread is treated with saturated and nonsaturated steam and, in the case illustrated, air; 12 is the pipe through which the steam arrives and which is provided at its end with a plurality of holes 13; 14 is a fan; 15 indicates the pipe for delivery of air. 24 and 25 indicate two thread-guides.

The steam leaving the pipe 12 through the holes 13 is admixed with the air coming from the fan 14 in a vestibule 16 and, passing through a perforated wall 17, contacts the filaments 18. Leaving the chamber 11 the filaments run through the space 19 which is preferably tubular and is provided with a jacket 20 for heating by means of fluids. It is self-understood that said tube 19 may be heated by any means whatsoever, such as for instance by means of an electric resistor.

On leaving the tube 19, the filaments pass through the second thread-guide 25 and are then stretched with the aid of mechanical means known per se, such as for instance in two steps by means of three pairs of skew cylinders 21, 22 and 23 having different peripheral speeds, and are finally wound up on the bobbin 26.

Example 1 A polycapronamide yarn of relative viscosity 2.7 was extruded and collected in the usual way without stretching, cooled with cold air at its issuance from the spinneret and subsequently passed into a tube 15 metres long at room temperature, to wind it up on a bobbin without stretching.

The yarn so obtained, after conditioning for 12 hours at temperatures and relative moisture respectively of 22 C. and 66% U.R., was then stretched by usual devices having pairs of skew rolls, in two stages. -It was collected and its properties were determined.

The characteristics of said yarn are reported in Table 1. It appears that the number of failures was very low, the tenacity was good and the elongation was satisfactory.

By spinning speed is understood in this case the speed of collecting the non-stretched yarn on the bobbin.

Such a yarn displays the characteristics as desired for a yarn of that kind.

Example 2 The same yarn as obtained in Example 1 was stretched continuously after spinning, namely without collecting the non-stretched layer, but merely passing it over a pair of guide rolls from which it passed to the stretching devices. In this case the spinning speed was the linear speed of the yarn over the guide rolls.

Here too the stretching was in two steps.

The results are tabulated in Table 2. It appears that as long as one operated with low stretching'ratios, one obtained a yarn with excessive elongation and low tenacity, with a large number of failures, but that it was not possible to arrive at normal stretching ratios because the num- Example 5 The operation was carried out as in Example 4 keeping in the treating chamber 11 a relative moisture of 90% and a temperature of 50 to 55 C. and in the accompany- 5 ing tube a temperature of 60 C. gsf g ggs gi gi ggi g and the operatlon be A glossy polymer of nylon 6 was spun having a rela- The results of Table 2 therefore show how by effecting gig 3 gi fi sag gg g? 23 3; the stretching continuously with respect to the spinning 500 met es g g; Th t'otal Stretchin f; was while operating by usual methods, very bad, industrially 1O g gfi d i Ste 8 g: first of unacceptable are obtained. 1 e o p 1 e 0 TABLE 1 Spinning Stretching ratio Count Elon- No. of Regular- Total S eed, filament, Tenacity, gation, failures ity of Tests No. Count 111 min. I den. grJden. percent per kg. count 1 1.200 250 1:3.8 1:1.18 5. 95 5.6 32 0.1 13.5

TABLE 2 Spinning Stretching ratio Count Elon- No. of Regular- Total S eed, filament, Tenacity, gation, failures ity of Tests No Count m min. I H den. grJden. percent per kg. count 1 1.200 250 1;2.s 1:1.12 6.3 I 3.7 95 4.5 :l:6 2 1. 200 250 1:3 1:1.18 6. 1 4. 2 60 25. 0 5:1.5

- Example 3 which the stretching is 123.8 and in the second one 1:1.32. I 0

The operation was camed out as m Example 2, but 0 i ii 2 li iz f g s the yarn was introduced into the tube or treating chamber 3 y 0 S 3 2 e t ea 18p g 11 which was ten metres long, condensed saturated steam, a 2 erage e onga Ion o 0 an a enacl y o the relative moisture in the tube being 90% and the E 1 6 temperature therein being '60 C. -The results obtained Xamp c with different stretching ratios are collected in Table 3. i The operation was carried out under the conditions of It appears that the number of failures is sensible also here Example 4 as regards the treatment of the thread at the and it is not possible to attain normal stretching ratios, time of extrusion. A polymer was spun of nylon 6 having owing to the increase of the number of said failures. The relative viscosity (in sulfuric acid) of 2.6-2.7 in the count tenacity remained'substantially below a good commercial of 100 den. with 28 filaments at a guide speed of 250 tenacity. t metres per minute. The stretching ratio (stretching having I v TABLE 3,

Total Filament Spinning Stretching ratio Elon- No.01 Regular- Count, count, 5 eed, Tenacity, gation, failures ity of Tests No. den den m. min. I gin/den. percent per kg. count 1, 050 6.0 250 13.7 1=1.2 4.4 a 3:4 1, 300 6.0 250 nae 1=1.2 4.9 42 20 :l:3.5 1, 200 20. 0 250 1:3. 8 1:1. 2 4. 5 30 3.13.5

Example 4 45 been carried out in the conventional way but successively) The operation was carried out according to the invention, under the following conditions:

The thread of nylon 6 extruded in the spinneret is treated with air having 95% relative moisture and at a temperature of C., in a treating chamber ten metres long. After that treatment the yarn passes into a tube fifteen metres long and surrounded by a heating jacket adapted to maintain in said tube a temperature of C The yarn is collected and the results obtained are listed in Table 4. If the spinning speed is taken into account, which here too indicates the speed of the yarn on the guide-rolls, and so the stretching ratios, the stretched yarn is collected with a speed that may be near to 2000 metres/ minute and even exceed this value.

was 1:45.

The number of failures/kg. of yarn is 0.05 while the instantaneous regularity of count is :11.5%.

The yarn obtained shows on analysis an average elongation of 35% and a tenacity of 6 gr./ den.

Example 7 TABLE 4 Instantane- OIIS regu- Total Filament Spinning Stretching ratio Elon- No. of lerity eoun coun speed, Tenacity, gation, failures 01 count den. den mJmin I II gin/den. percent per kg. 450 3. 0 400 1:3. 5 1:1. 20 5. 0 2. 5 840 6. 0 250 1:3. 7 1:1. 20 6. 0 1.0 840 6.0 500 1:3.5 1:1. 20 5.9 2. 0 1, 100 15. 0 450 1:3. 8 1:1. 20 6. 8 2. 5 1, 200 20. 0 450 1:3. 8 1:1. 25 7. 0 2. 5

From the same table one sees how the tenacities obtained are elevated, 7 gr./den. being easily attained with normal elongations and good regularity of count. The number of failures is very low and is in some cases completely irrelevant.

The number of failures/kg. of yarn was 0.04 while the instantaneous reguarity of count was 21%.

Hence, by the process of the present invention with spinning and immediately successive stretching results are obtained at least equal to and often better than those obtainable by the discontinuous process, contrary to what was known heretofore.

Of course the preceding working examples have no limiting character, since many variants can be introduced by the skilled in the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for producing continuously filaments of polyamides and polyesters, obtained by melt-spinning, comprising the stepsof producing filaments by extrusion from a spinneret, feeding the filaments from the spinneret directly into a medium containing steam at a temperature of from 30 C. to 200 C., forwarding the extruded filaments in said medium in such a way that they are subjected, for at least one second, to treatment by steam at a temperature not exceeding 100 C. in the presence of air, the proportions of steam and air being such that the air has a relative moisture of at least 85%, then passing said filaments into a heated space, having an internal temperature of from C. to 95 C., in which all portions of the filaments remain for at least one second, and immediately subjecting the filaments to a mechanical stretching treatment with a stretching ratio between 1:3.5 and 1:5 after issuance of the filaments from said heated space,

2. A process according to claim 1, wherein the treatment with steam continues for from one second to six seconds.

3. The process according to claim 1, wherein the heated space is heated to a temperature of from 60 C. to 70 C.

4. The process according to claim 1, wherein every portion of the filaments is kept in said heated space for from one to six seconds.

5. The process according to claim 1, wherein the filaments are subjected to the stretching in two successive steps, at first at a lower linear speed and then at a higher linear speed, the lower linear speed corresponding substantially to the linear speed of the filaments at the outlet of said heated space.

6. The process according to claim 1, wherein the filaments treated are polycapronamide filaments.

7. A process according to claim 5, wherein the treated yarn is a polycapronamide, is subjected at the outlet of the spinneret to air with from 90 to 95% of relative moisture and to a temperature of from to C. and then is passed through a medium heated to a temperature of from 60 to C., is then subjected to a first mechanical stretching with a stretching ratio of from 1/ 3.5 to 1/3.8 and to a second mechanical stretching with ratio of from 1/ 1.2 to 1/ 1.32 said treatments beingv carried out in succession and continuously, to obtain \a treated yarn having a tenacity of from 5 to 9 gr./dem'er.

8. A process for the production of yarns of polycapronamide having high tenacity, wherein the yarns are subjected, immediately on their extrusion from a spinning head, to a treatment in a medium having a relative mois ture of at least and a temperature of at least 50 C., for from one second to three seconds, then are forwarded continuously in a second heated medium at a temperature of at least 60 C. and kept in said second medium for from one second to six seconds, and thenare immediately subjected to a mechanical stretching treatment.

9. A process according to claim 8, wherein the polycapronamide yarn is subjected to a stretching treatment with total elongation ratio of from A to /5.

References Cited UNITED STATES PATENTS Babcock 264-210 DONALD I ARNOLD, Primary Examiner.

U.S. Cl. X.R. 264--176, 290 

